1. Field of the Invention
The present invention relates to a method of reducing the surface tackiness of a silicone rubber cured product, an addition reaction curable liquid silicone rubber composition for sealing semiconductors, and applications of that composition. In other words, the invention relates to applications such as a silicone rubber-sealed semiconductor device that uses the above composition as a sealing material for a semiconductor element, and a method of producing such a device.
2. Description of the Prior Art
Silicone rubber compositions form cured products that exhibit excellent properties of weather resistance and heat resistance, and excellent rubber-like characteristics such as hardness and elongation, and are consequently used in all manner of applications. Furthermore, because excellent heat resistance and light resistance can be achieved by coating a target product with a silicone rubber, silicone rubbers are also being investigated as potential materials for all manner of packages.
The sealing (molding) of semiconductor elements using silicone cured products is already being conducted, but amongst the various possible silicone cured products, hard resins tend to be prone to cracking or bonding wire deformation problems, whereas soft rubbers exhibit surface tackiness, meaning they tend to be prone to dirt adhesion, and also suffer frequently from adhesion of the sealing resin (the molding resin) within the parts feeder. A common countermeasure to these problems is a method in which a soft rubber or gel is used as an inner material, and the exterior of this inner material is then coated with a hard rubber or hard resin (patent reference 1). However, in this method, because the soft rubber or soft gel usually retains small quantities of residual vinyl groups within the cured polymer, it tends to be affected by the exterior hard rubber or hard resin, meaning the inner soft rubber or gel gradually hardens over time, increasing the likelihood of bonding wire breakage or deformation.
[Patent Reference 1]
U.S. Pat. No. 5,279,890